why earthquick comes?

Answer 1

It all comes down to stress and strain. It is not 'the plates rubbing together' as many people say; or at least that's a very simplistic view.

Plate tectonics causes stress on the continents and oceans, all over the surface of the earth. In some places, the stress is very small (usually within the plates). Elsewhere, the stress is high, usually where the plates meet each other. Since each plate moves, when two come in contact, the stress each other. They can push on each other and cause compressional stress, they can pull with extensional stress, and they can slide past or shear each other with tensional stress.

Faulting, causing earthquakes, comes from the fact that this stress is building up all the time, but rocks and continents are strong materials. Just like hitting a rock with a small hammer, you do put stress on it, but a small amount. It would take a sledgehammer to put enough strain (effects and accumulation of stress) to build up and cause breakage. In the earth, the area around an active fault builds up strain from the stress of plate tectonics. Most faults become locked, because of this strength, and thus can not release their strain. Away from the fault, the stress produces very small and slow movement of the rock masses as a whole. Eventually, the strain is too much and the rest of the plate has moved too far and the fault releases the strain build-up all at once in a big stress release called an earthquake. This is called the elastic rebound theory, and it explains most (but not all) movements.

This is why an earthquake's size is relative to the fault size. The bigger the fault, the bigger the strain build up, and the bigger the release in an earthquake. Subduction zones and collision zones, where large portions of plates actually can rub together as a whole, have the really big earthquakes, like the 2004 Sumatra earthquake. In other plate boundaries, the entire plate boundary does not act together, so the faults become spread out and many faults take up the strain from the tectonic stress, like with the San Andreas Fault in California (it only takes up ~3/4 of the stress between the plates).

Earthquakes are really tricky things; there is still so much we need to learn. As of now, there is no way to predict them, but we can say where the danger is highest and about how long between events.

Answer 2

What causes earthquakes?

The short answer is that earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a rupture (break) surface.

Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motion of immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each other in some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other (like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the edges are distorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. An earthquake is the shaking that radiates out from the breaking rock.
People have known about earthquakes for thousands of years, of course, but they didn't know what caused them. In particular, people believed that the breaks in the Earth's surface--faults--which appear after earthquakes, were caused *by* the earthquakes rather than the cause *of* them. It was Bunjiro Koto, a geologist in Japan studying a 60-mile long fault whose two sides shifted about 15 feet in the great Japanese earthquake of 1871, who first suggested that earthquakes were caused by faults. Henry Reid, studying the great San Francisco earthquake of 1906, took the idea further. He said that an earthquake is the huge amount of energy released when accumulated strain causes a fault to rupture. He explained that rock twisted further and further out of shape by continuing forces over the centuries eventually yields in a wrenching snap as the two sides of the fault slip to a new position to relieve the strain. This is the idea of "elastic rebound" which is now central to all studies of fault rupture.

Answer 3

About 90% of the worlds earthquakes occur at the boundaries between techtonic plates and the other 10% are what we call intracontinental (occur inland without any known fault structures present...sometimes the result of the extraction of one or more of the earth's natural resources like crude oil).

Those occuring at techtonic boundaries happen on one of three types of faults : Strike-slip faults where two plates are moving horizontally past each other like the San Andreas, Subduction faults where one plate is being pushed under another like in the Cascadia Subduction Zone in the Cascadia mountain range in the north-western US (these are usually accompanied by volcanos), and thrust faults where one side of the rupture is pushing vertically (up or down) relative to the other (this often forms low rolling mountains like the Transverse Ranges in southern California).

The movements of all of these techtonic plates are caused by convection currents in the earths mantle (imagine a pot of boiling water with spaghetti noodles; the noodles are being pushed in an upward and outward fashion).

However, just because the plates are moving doesn't mean there are neccesarily going to be earthquakes. Some faults experience "fault creep". Let's take the San Andreas for instance: The northern 300 miles of the fault ruptured in the great San Francisco earthquake of 1906 and the southern or Mojave section last ruptured about 250 - 300 years ago yet the middle section of the fault (near Hollister, CA) has been slowly creeping along without much or any earthquake activity.

The Cascadia subduction zone is one of the least active subduction zones in the world causing most of its seismic activity through volcanis vents and only rupturing on a grander scale every couple of hundred year. Earthquakes in Japan are generally caused by subduction fault zones and are much more common than in Cascadia.

Note: The 2004 Indian Ocean tsunamis were caused be a rupture on a subduction fault zone about the same length as the Cascadia subduction zone.

Answer 4

earthquakes occurs naturally or someitmes induced ..

Natutal earthquakes are called Tectonic quakes.Earth's lithosphere is a patch work of plates in slow but constant motion caused by the heat in the Earth's mantle and core. Plate boundaries glide past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's crust, the elastic strain energy is released and elastic waves are radiated, thus causing an earthquake.

Some earthquakes have anthropogenic sources, such as extraction of minerals and fossil fuel from the Earth's crust, the removal or injection of fluids into the crust, reservoir-induced seismicity, massive explosions, and collapse of large buildings. Seismic events caused by human activity are referred to by the term induced seismicity

For more info U can visit the website :

http://en.wikipedia.org/wiki/Earthquakes

Answer 5

Most earthquakes are causally related to compressional or tensional stresses built up at the margins of the huge moving lithospheric plates that make up the earth's surface (see lithosphere). The immediate cause of most shallow earthquakes is the sudden release of stress along a fault, or fracture in the earth's crust, resulting in movement of the opposing blocks of rock past one another. These movements cause vibrations to pass through and around the earth in wave form, just as ripples are generated when a pebble is dropped into water. Volcanic eruptions, rockfalls, landslides, and explosions can also cause a quake, but most of these are of only local extent. Shock waves from a powerful earthquake can trigger smaller earthquakes in a distant location hundreds of miles away if the geologic conditions are favorable.

Answer 6

Hi. The Earth is changing all the time. One of these changes is that the core, which is very hot and is actually melted, moves. What you see as the Earth is really only lighter stuff (compared to the iron which makes up a lot of the core) called the crust floating on top. As the core and the outer regions of it, called the mantle, move they move the crust (rock and water mostly) around. Sometimes this happens smoothly but sometimes the movement gets stuck for a while. Pressure and stress build up until the crust moves again and when it does, we have an earthquake.

Answer 7

Earthquakes are caused, when two plate boundries rub againts each and they get stuck the pressure builds up and when a brake happens an earthquake is the resualts.

Answer 8

It is earthquake dear! and they come due to shifting of tectonic plates(under earth surface, not in my crockery cupboard)

Answer 9

in accordance to the theory of tectonics-..they occur due to the movement of the tectonic plates

Answer 10

To give justice to people for their bad deeds.